Field
The present disclosure generally relates to a power transmission apparatus that wirelessly transmits power to a power receiving apparatus.
Description of the Related Art
In recent years, there has been known a wireless power transmission system including a power transmission apparatus including a primary coil for wirelessly supplying power without being physically connected via a connector, and a power receiving device including a secondary coil for wirelessly receiving the power supplied from the power transmission apparatus. In the wireless power transmission system, if a foreign substance, such as a metal object and an IC card, is arranged between the primary coil and the secondary coil, or near these coils, the power supplied from the primary coil can be supplied to the foreign substance and the foreign substance can be damaged.
Japanese Patent Laid-Open No. 2014-126512 discloses a technique of using a detection coil including a figure of eight formed in such a manner that induction currents flow in opposite directions when a magnetic flux circulating between a primary coil and a secondary coil passes through the detection coil. In this technique, a metal object is assumed to be detected based on a change in impedance of the detection coil.
In the technique described in Japanese Patent Laid-Open No. 2014-126512, the uniformity of magnetic field intensities within the detection coil is not mentioned. In the detection coil including a figure of eight, in which induction currents flow in the opposite directions when the magnetic flux circulating between the primary coil and the secondary coil passes through the detection coil, the magnetic field intensities within the detection coil do not become substantially uniform. Thus, the impedance varies depending on a position where a power receiving device including a metal object is arranged in a housing structure, and it cannot be determined whether a foreign substance has been detected or the position of the power receiving device has merely shifted.